1. Field of the Invention
The present invention relates to a probing apparatus for testing the electric characteristics of semiconductor chips formed on a semiconductor wafer by bringing probes for sending and receiving electric signals into contact with electrode pads of each semiconductor chip. In particular, the present device relates to a probing apparatus in which it is easy to replace a probe card with another one depending on a semiconductor wafer to be tested. The present device also relates to a semiconductor wafer testing system employing the probing apparatus.
2. Description of the Related Art
Semiconductor chips are usually formed by cutting a single crystal of silicon into a thin wafer, etching the surface of the wafer into circuit patterns, and cutting the wafer with a dicing machine into the chips. Before cutting the wafer on which the circuit patterns have been formed with the dicing machine, the electrical characteristics of the semiconductor chips on the wafer are tested by a probing apparatus, to check for defective chips. In the following, the test of the electrical characteristics of semiconductor chips formed on the wafer is called a test of electrical characteristics of the wafer or only a wafer test.
To test the electrical characteristics of a wafer, the probing apparatus uses a circular probe card having probes suitable for circuit patterns of chips formed on the wafer. The probe card is fixed to a pin socket such as a pogo (TM) pin socket, which is connected to a tester in the probing apparatus. The probes of the probe card are brought into contact with the wafer to test the wafer. The probe card may be changed with another one depending on the kind of wafer to be tested. According to a prior art, an operator must manually unfasten screws of the probe card to replace it with another one.
In this case, there is a risk of damaging probes of the probe cards while the operator is manually changing the probe cards with each other. Accordingly, there is a need for automating the wafer testing work. FIG. 1 shows a probing apparatus 11 proposed in Japanese Unexamined Patent Publication No. 63-280431. In FIG. 1, reference numeral 1 designates a probe card, reference numeral 4 designates a wafer chuck, reference numeral 9 designates a wafer, reference numeral 11 designates a probing apparatus within a casing, reference numeral 12 designates a probe card cassette, reference numeral 14 designates a wafer cassette, reference numeral 16 designates a control panel for controlling the probing apparatus. Actually, the wafer chuck 4 and the wafer cassette 14 etc., are not visible from outside, however, for convenience, they are shown as FIG. 1. A few of the other figures are also shown in this way. Further, in the figures, same portions are designated by the same reference numbers.
This probing apparatus 11 of FIG. 1 has a probe card cassette 12 for storing various kinds of probe cards 1 from among which one suitable for a semiconductor wafer to be tested is selected and automatically set.
The present applicant has proposed, in Japanese Unexamined Patent Publication No. 3-220742, an improvement in the above probing apparatus. This improvement uses a semiconductor wafer moving mechanism as the probe card moving mechanism, thereby realizing a simple structure. This semiconductor wafer moving mechanism includes a wafer chuck which holds the wafer by vacuum pressure.
In the probing apparatus shown in FIG. 1, there is no risk of damaging probes of the probe cards while the probe cards are being exhanged with each other because the operation is performed automatically. However, this probing apparatus has problems in that size of the apparatus becomes large and total efficiency of the use of the probe cards held in the cassette decreases.
In recent years, semiconductor devices are being integrated more and more and, therefore, probing apparatuses must carry out more complicated and time-cosuming tests of the semiconductor devices. The size of each semiconductor wafer is also increasing to improve productivity. Namely, the number of chips per wafer is increasing. This is another factor in elongating the testing time of each wafer.
The probing apparatus is designed to deal with various kinds of semiconductor wafers. In actual semiconductor production lines, however, the kinds of semiconductor wafers are not frequently changed from one to another. Namely, once a probe card is set, it will not to be replaced with another for a long time.
Actually, even in the probing apparatuses according to Japanese Unexamined Patent Publication Nos. 63-280431 and 3-220742, probe cards are not frequently switched from one to another. In this case, many probe cards held in the cassette are not used but are only stored for a long time.
Since it takes a long time to test a semiconductor wafer, a factory having a certain extent of production scale runs many probing apparatuses in parallel. If each of the probing apparatuses must store many probe cards, a great number of probe cards are not actually used, so the efficiency of use of the probe cards will be very low.
Further, each apparatus must be very large and complicated because it has to accommodate many probe cards although a great part of those probe cards are not used.